The long-term objective of the proposed research is to elucidate the molecular basis of monocyte endothelial cell interactions, and to understand the mechanism of the increased adherence of monocytes to endothelial cells in the earliest stages of atherosclerosis. Data from several laboratories indicates that circulating monocytes are the precursors of the lipid-laden foam cells found beneath the endothelium in cholesterol-fed experimental animals. Yet, little is known of the regulation or molecular mechanism involved in monocyte adherence to endothelial cells. Work over the past 2 years has defined a superfamily of adhesive protein receptors, the "Integrins", which mediate a number of cell-cell and cell-substrate interactions. For example, platelet aggregation is mediated by the GP Ilb-IIIa complex, and fibroblast adhesion to fibronectin by the fibronectin receptors. In the current proposal, experiments will be performed to identify the integrin-type adhesive protein receptors on-human monocytes, and monocyte-derived macrophages, and to determine if these receptors mediate the increased adherence of monocytes to endothelial cells in hypercholesterolemia. Newly developed cDNA probes and monospecific antibodies (monoclonal and polyclonal) will be used to measure the synthesis and expression of the known integrins in both normal human monocytes and monocyte- derived macrophages, and those that have been cholesterol-loaded. The functional role of integrins in mediating adhesion will be examined using antibodies against the integrin adhesive protein receptors in a quantitative centrifugation assay of monocyte adherence to endothelial cells. Monoclonal antibodies will be raised against both normal and cholesterol-loaded monocytes to look for additional receipts that might mediate monocyte-endothelial cell interactions in hypercholesterolemia. I will also examine monocytes obtained from patients with genetic disorders and beta- VLDL to determine if they express increased numbers of adhesive protein receptors. The proposed research should increase our knowledge of the molecular mechanisms of monocyte-endothelial cell interactions and may form a basis for the design of rational and novel strategies to prevent and treat atherosclerosis.